1. Field of the Invention
The present invention relates to an angle-adjusting device for a treadmill frame, and more particularly to an angle-adjusting device that makes the treadmill stable and vibrate less during operation.
2. Description of Related Art
With reference to FIG. 6, a conventional angle-adjusting device (50) for a treadmill frame in accordance with the prior art is adapted to be secured under the rear end of a treadmill. The treadmill (40) includes a front supporting lever (41), an erect handgrip frame (42), a belt frame (43), a traveling belt (45) and the angle adjusting device (50). The angle-adjusting device (50) is composed of a pair of polygonal feet (51) respectively mounted on opposite sides of the bottom of the rear portion of the belt frame (43). The polygonal feet (51) are triangular. The polygonal feet (51) are respectively rotatably mounted on opposite ends of a connecting rod (46).
Each polygonal foot (51) has multiple ground contact edges (not numbered), and each edge is a different length from the other edges so when any ground contact edge of the polygonal plate (51) contacts the ground, the sloping angle of the belt frame (43) is changed. Furthermore, changing the sloping angle of the belt frame (43) only requires raising the belt frame (43) to allow the ground contact edge of each polygonal plate (51) to be lifted clear of the ground. Thereafter, the two polygonal feet (51) are rotated on the connecting rod (46) to permit another ground contact edge to be parallel to the ground. Since the ground contact edge of the polygonal plate is changed, the sloping angle of the belt frame (43) can be easily changed to meet different requirements.
However, the conventional angle-adjusting device (50) is not directly secured on the belt frame (43), and a xe2x80x9clinkage,xe2x80x9d as show in FIG. 7, is formed between the angle-adjusting device (50) and the belt frame (43) in mechanics. The treadmill having a conventional angle-adjusting device (50) constitutes three links of a quaternary link, wherein the four links of the quaternary link are the angle adjusting device (50), the belt frame (43), the front supporting lever (41), and the ground. Stability of this linkage can be estimated by the Kutzbach formula:
F=3(Nxe2x88x921)xe2x88x922P 
Wherein F is the degree of freedom of the kinematic chain;
N is the number of links; and
P is the number of pairs of elements.
Where N=4 and P=4 for the conventional quaternary link, F is 1. When F is positive, the kinetic chain being analyzed is under-constrained (i.e. moveable) according to the Kutzbach formula. Since F is positive for this quaternary link, the treadmill is unstable and will vibrate when someone steps or runs on the structure.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional angle-adjusting device.
A main objective of the angle-adjusting device in accordance with the present invention is to make the treadmill stable during operation.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.